You can use this function safely with your MySQL database queries if and only if you are sure that your database connection is using ASCII, UTF-8, or ISO-8859-* and that the backslash is your database's escape character. If you're not sure, then use mysqli_real_escape_string instead. This function is not safe to use on databases with multi-byte character sets.
The only benefit of this function is that it does not require a database connection.